1. Field of the Invention
This invention relates to a method for inspecting the stripped condition of electric wires.
2. Statement of the Prior Art
Conventionally, it is known that the stripped condition of a tip of electric wire, for use in wiring harnesses or the like, is inspected by means of a conductibility inspection method. For convenience of illustration, such a method will be explained below with reference to FIGS. 13, 14 and 15. FIG. 13 is a schematic circuit diagram for a prior art conductibility inspection method. FIG. 14 is a view illustrating operation of the conductibility inspection method. FIG. 15 is a view illustrating various stripped conditions of electric wires.
As shown in FIG. 13, a prior art conductibility inspection circuit includes a battery 1, a resistor 2 and a light emitting diode 3, all connected in series. The conductibility inspection circuit is connected at one end thereof to a conductor of an electric wire 4, and connected at the other end to a contact 5. The contact 5 is contacted with a core 6 of the electric wire 4 which has been stripped of its cover so as to check if the light emitting diode 3 will be lighted due to the electric current through to the light emitting diode 3 in the conductibility inspection circuit. When the tip portion of the electric wire 4 has been stripped of its cover to some extent, the core 6 and contact 6 are securely contacted with each other, so that the light emitting diode 3 will be lighted.
Thus, it is determined that the stripped condition of an electric wire is "good" when the light emitting diode 3 is lighted. On the other hand, if the light emitting diode 3 is not lighted, it is determined that the stripped condition of the electric wire is "not good" or "poor".
Another method for inspecting the stripped condition of electric wire is shown in FIG. 14. According to this method, a box 7 housing therein a light source and an additional box 8 in opposed relation to the box 7 are provided. The box 7 is formed with two slits 9a and 9b. The box 8 includes light receiving elements at positions opposite to the slits 9a and 9b, respectively. Electric wire 4 is moved at a constant speed between the boxes 7 and 8 in a manner such that a core 6 of the wire will block a beam of light from one slit 9a, while the sheath of the wire will block a beam of light from the other slit 9b. A cross-sectional area of the core 6 having been stripped off can be calculated using the variations in waveform of output signals from the light receiving elements, so that the stripped condition of the wire may be determined.
With the above method, it is merely determined whether or not the tip portion of the wire 4 is stripped of its sheath so as to expose its core. It is, however, not possible to determine the shape or configuration of the core 6, i.e., length or thickness of the core exposed or stripped off.
Another method for inspecting stripped condition of electric wire is also known, which utilize a picture processing technique. For example, Japanese Patent Public Disclosure No. 57-198850 discloses a method for inspecting looseness of sheath material and deviation of stripped position by a binary processing of a picture obtained from a one-dimensional image sensor. Japanese Patent Public Disclosure No. 59-216044 also discloses an inspection method in which collimated light is illuminated onto a tip portion of a wire which is clamped, the shade behind the wire is received by a one-dimensional light receiving means oriented perpendicularly to the wire, and moving the light receiving means along the length of the wire so as to determine the good or not good condition of the wire end on the basis of light information received by the light receiving means.
It is noted, however, that, actually, a tip portion of a stripped wire 4 may take a various configuration as shown in FIG. 15. For example, the tip portion may have strands coming out, dispersion, or expansion of a core (a, b and c, respectively), defects in sheath (d), deformation of a core (e) and the like. These shapes may cause a problem during installation of a crimp-style terminal thereon, so that such wires should be determined to be in a not good stripped condition. The above method utilizing conventional picture processing technique is incapable of detecting such detailed configuration of the tip portion of wires as mentioned above, so that they are disadvantageous in carrying out inspection with high accuracy and reliability.